feat(plan): add Plan tab as the first project surface

A new home for everything that happens BEFORE building:
- Vision    — one-line elevator pitch (mirrors productVision)
- Ideas     — the "park-it" bin for raw thoughts
- Tasks     — what needs to happen next (open / done)
- Decisions — log of "we chose X over Y because Z"

Storage is appended under fs_projects.data.plan so no schema migration
is needed. CRUD lives at /api/projects/[projectId]/plan.

The bare project URL now redirects to /plan instead of /product, and
the AI chat receives decisions + open tasks in its active-project
context block — so it stops re-litigating settled questions and knows
what's queued up.

Made-with: Cursor

app/api/chat/route.ts

@@ -74,6 +74,32 @@ export function buildSystemPrompt(
   // at the top so the model treats `projectId` as resolved without the
   // user having to name it. Falls through to the workspace-level mode
   // (browse all projects) when activeProject is undefined.
+  // Pull plan artifacts (decisions + open tasks) so the AI doesn't ask
+  // the user to re-decide settled questions and knows what's queued up.
+  // Decisions are first-class: they encode the founder's intent and
+  // should be honored unless the user explicitly revisits one.
+  const plan = (activeProject?.plan ?? {}) as {
+    decisions?: { title: string; choice: string; why?: string }[];
+    tasks?: { text: string; status: "open" | "done" }[];
+    ideas?: { text: string }[];
+  };
+  const decisionsBlock = plan.decisions?.length
+    ? `\n**Decisions already made for this project (DO NOT re-litigate unless the user asks):**\n${plan.decisions
+        .slice(0, 20)
+        .map((d) => `- ${d.title} → ${d.choice}${d.why ? ` (because: ${d.why})` : ''}`)
+        .join('\n')}\n`
+    : '';
+  const openTasks = (plan.tasks ?? []).filter((t) => t.status === 'open').slice(0, 15);
+  const tasksBlock = openTasks.length
+    ? `\n**Open tasks the user has captured:**\n${openTasks.map((t) => `- ${t.text}`).join('\n')}\n`
+    : '';
+  const ideasBlock = plan.ideas?.length
+    ? `\n**Ideas parked (not commitments — surface only if relevant):**\n${plan.ideas
+        .slice(0, 10)
+        .map((i) => `- ${i.text}`)
+        .join('\n')}\n`
+    : '';
+
   const activeBlock = activeProject
     ? `\n## ACTIVE PROJECT — assume this for every tool call unless the user explicitly says otherwise
 
@@ -84,7 +110,7 @@ The user is currently looking at:
 - Audience: ${activeProject.audience ?? 'unspecified'}
 - Vision: ${activeProject.productVision ? activeProject.productVision.slice(0, 240) : '(not yet captured)'}
 ${activeProject.kickoff ? `- Created via: ${activeProject.kickoff.mode} (${JSON.stringify(activeProject.kickoff.sourceData).slice(0, 200)})` : ''}
-
+${decisionsBlock}${tasksBlock}${ideasBlock}
 When you call tools that take a \`projectId\`, USE this id (\`${activeProject.id}\`) without asking. When the user says "this project" / "the app" / "deploy it" — they mean THIS project. Switch to a different project only if the user names one explicitly.\n`
     : '';